[Cryptech Tech] User auditable hardware entropy source/random number generator

[Benedikt Stockebrand]

Hi folks,

Bernd Paysan <bernd at net2o.de> writes:

> Am Donnerstag, 10. Juli 2014, 22:44:43 schrieb Leif Johansson:
>
>> Yeah there is no use for _low_ noise zener diodes ;-) Next they'll go
>> after amplifiers ... the bastards !

and the vendors are all in cahoots with them---you won't find any
statement of *minimum* noise levels in any datasheets.  It's a global
conspiracy:-)

Anyway, one of the reasons why I use general purpose transistors rather
than some sort of amplifier IC is actually because it'll be more
difficult to subvert these---seriously.

> Hm, for noise sources, you should use avalanche diodes, not zener diodes
> [...]

I do, but they are both *sold* as Zener diodes (at least with voltages
below 60V or so).  And yes, you have both the Zener and the avalanche
effect in all of them, but the higher the voltage the more predominant
the avalanche effect; that's why I need the 12V source.

>From tests with my lucky (i.e. ultra noisy) Zener/avalanche diode set,
at 6.8V breakdown voltage the avalanche effect gets strong enough to be
useful as a noise source.  With 6.2V or less the noise becomes very low
amplitude while with higher voltages the frequency spectrum shifts down,
effectively reducing the output speed.

Anyway, since I've had such inconclusive results with different
BZX55C6V8 diodes, apparently either from different manufacturers or with
the extra crappy ones being sold in those sets, I'm just about to resort
back to a three transistor design again.  Doing so should make the
design more complex but way more robust with regard to this problem.


Cheers,

    Benedikt

-- 
Benedikt Stockebrand,                   Stepladder IT Training+Consulting
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